Description

Guanylate cyclase-activating proteins (GCAPs) are calcium binding proteins that belong to the calmodulin superfamily. GCAPs without calcium are responsible for activation of photoreceptor guanylate cyclase during light adaptation. Studies have shown that the addition or subtraction of Ca2+ results in major conformational changes and the activation/deactivation of GCAP 1 and GCAP 2. It has been demonstrated that both GCAP 1 and 2 act on guanylate cyclase similarly and have approximately 50% homology between the two forms. GCAP-1 is predominantly localized in the photoreceptor outer segments, while GCAP 2 is found in retina samples.